Heating and Air Conditioning (HVAC) systems for modern buildings and factories are generally precisely regulated to control the amount of outside air introduced into the system. In such systems, the designer must balance the need for energy conservation, which entails minimizing the amount of new outside air which must be introduced, and therefore heated or cooled, vs. the competing need for adequate fresh air ventilation to prevent the accumulation of stale air and the accompanying effects of so-called "sick building syndrome" on occupants.
Typically, in such controlled HVAC systems, outside air is introduced via selectively controllable dampers. For example, a damper can be a rectangular frame built into a wall communicating with the exterior of the building. Within the rectangular frame, a plurality of rotatable vanes are positioned, which vanes are selectively rotatable between a vertically oriented, completely closed position at which no air is introduced, and a substantially horizontally oriented, completely open position at which maximum air is introduced. Between these extreme positions are an infinite number of intermediate, partially open positions.
In order to accurately control the amount of ambient air introduced into a building, the air flow must be measured. A number of attempts have been made to associate pitot-static air flow sensing vanes with controllable dampers. A problem with the association of air flow sensors with dampers is the requirement for the sensors to be considerably removed from the damper to eliminate the effects from air flow turbulence created by the damper. Typically, with discrete dampers and air flow sensors, the minimum separation required is at least 2-3 diameters, i.e. 2-3 times the equivalent round diameter of the duct within which the damper and sensor is positioned. This separation is unacceptable in many applications and renders it difficult, due to the extended length, to place damper and sensors in a common housing.
It is clear then, that a need exists for a combined air flow measurement station and damper which can be included in a common housing of reasonable length and bulk. Such an air flow measurement station should allow accurate measurement of air flow through the damper without regard to damper blade position and turbulence.